Studies done in animals and in humans have suggested that the natural history of diabetic kidney disease can be altered by changing renal hemodynamics and function using enalapril. This study will test these hypotheses. Patients will be randomized to two groups in a double blinded study. These groups will consist of placebo/enalapril. Their kidney function will be monitored at six-month intervals measuring protein excretion, 24 hour creatine clearance, and iothalomate.